🔍 Key Concepts

• Loop-scavenged two-stroke diesel engines often use the underside of the piston as a pumping space to pre-compress air. • Air drawn into the piston underside must come through some kind of one-way (non-return) inlet device rather than the cylinder ports. • Study the illustration to see which label is connected directly to the space below the piston rather than to the cylinder liner or exhaust side.

💭 Think About

• On the upward stroke, what happens to the volume under the piston, and how does that affect pressure and airflow direction? • Looking at the diagram, which labeled item clearly forms a check/inlet path into the lower space rather than into the combustion space above the piston? • Which option’s description does not make sense as a path into the piston underside—especially considering where the cylinder ports and any turbo/blower are located?

✅ Before You Answer

• Verify which label in the diagram is positioned so that it opens into the crankcase or pumping space under the piston. • Confirm that the device you pick would logically be a non-return (one-way) valve, allowing air in on the upstroke and preventing backflow on the downstroke. • Make sure you are not choosing the scavenging ports in the cylinder wall, since those supply air above the piston, not to its underside.